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Glossary 2

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SPILLAGE—Condition of flue gases failing to exit the venting system properly and instead slowing out of the relief opening of the draft hood and into the dwelling. Condition calls for immediate examination of appliance and venting system and corrective action.

SPILLAGE TEST—Method of detecting spillage. Flame or smoke applied at draft hood being blown out (away from draft hood) indicates spillage problem that should be remedied with out delay.

SPLAY—Beveled or sloping surface which terminates a masonry chimney; seals the flue; provides drainage slope for rain and snow. Also called wash. Recommended that gap (with flexible sealer) be maintained between flue liner and splay and that splay extend at least 2 1/2 inches beyond exterior chimney wall.

STACK EFFECT—The effects resulting from the warm air in buildings on a cold day being relatively buoyant, just as are the flue gases in a chimney or stack. Effects include pressure differences between inside and outside the building, airflow into the building in the lower stories and airflow out of the building in the upper portions.

STEEL LINED FIREPLACE—Masonry fireplace with prefabricated metal firebox which has all the components of traditional fireplaces; may have double walls to provide circulating air passage behind the fire chamber.

STOVE—Wood or coal stove. A freestanding solid fuel burning, room heating appliance intended to be operated with its door(s) closed, i.e. with a closed fire chamber. NFPA and most codes use the term solid fuel room heater for stoves.

STOVE BOARD—A prefabricated panel used as a floor or wall protector.

STOVE LINER—A layer of metal or brick placed immediately adjacent to a side or bottom of a stove, intended either to protect the main stove structure from getting too hot, or to insulate the combustion chamber, making it hotter and thus promoting more complete combustion. Liners are usually designed for easy replacement.

STOVE PIPE—or smoke pipe. Single-walled light gage (roughly .019 to .024 inches thick) metal pipe generally intended for use as chimney connectors.

SUBSTRATE—Catalytic combustor component which carries wash coat and catalyst. Must be inert, stable, porous material providing large surface area. Almost exclusively ceramic in solid fuel combustors.

SWEET GAS—Gas in its natural state containing such small amounts of sulfur that it can be used without purification processes.

TEE—Chimney connector or factory-built chimney component which provides a 90 degree turn in the venting system; has a removable plate at the bottom for inspection and chimney cleaning convenience.

TEMPERATURE DIFFERENTIAL—The difference in temperature between two areas, such as inside and outside the chimney or house. (Example, if it is 90 degrees F. outside the house and 70 degrees F. inside the house the temperature differential is 20 degrees F.)

THERM—100,000 British Thermal Units (BTUs)

THERMAL EFFICIENCY - Thermal efficiency is the measure of the efficiency and completeness of combustion of the fuel ONLY. Does not take into account the HEAT TRANSFER EFFICIENCY, which describes how effectively the heat is used after it is generated.

THERMAL MASS—The combination of an objects weight and its ability to absorb heat. Represents an objects capacity to act as a heat battery.

THERMOCOUPLE—A device consisting of two pieces of dissimilar metals joined together at one end (hot junction). When the hot junction is heated, the thermocouple produces DC voltage across the other end. Used to power thermoelectric gas valves.


THERMOPILE—A number of thermocouples connected in series to produce a higher voltage than a single thermocouple.

THERMOSTAT—An automatic device for regulating the temperature in a building by controlling the heating or cooling source or its distribution.

THIMBLE—A device to be installed in combustible walls, through which stovepipe passes, intended to help protect the walls from igniting due to stovepipe heat. A thimble by itself is not usually adequate. The simplest thimbles are simply metal or fire clay sleeves or cylinders.

THROAT—The narrow passage above the fire chamber of a fireplace, forward of the smoke shelf and below the smoke chamber, generally has a damper which must be opened before the fireplace is used, and may be closed, when the fireplace is not in use.

TRIVET—Usually made of cast-iron, forged steel or ceramic, these are placed on top of the stove surface and allow for a tea pot or other item to be placed on them. Because they are usually set 1/2” or so above the stove surface, the temperatures will be a little lower than the stove surface itself. Trivets also prevent spillage and excess scratching of the stove surface.

TYPE B-W GAS VENT—A listed, factory built, oval shaped, double wall metal pipe for venting (only) vented wall furnaces.

U.L. LISTED—Underwriters Laboratories, Inc. 333 Pfingsten Road, Northbrook IL, 60062. An independent not-for-profit organization testing for public safety.

UNVENTED ROOM HEATER—category of unvented, self-contained, free standing, non recessed (except as noted) fuel gas burning appliance for furnishing warm air by gravity or fan without duct connection. Gas hearth appliances listed to ANSI Standard Z21.11.2 include Gas Fireplaces and Fireplace Inserts.

VALVE OPERATOR—Part of automatic valve that activates the flow of gas to the main burner, usually powered electrically. Also known as operator head.

VENT ORIFICE—Part of a pressure regulator, located in the chamber above the diaphragm. An opening which allows for the free flow of air in and out in the area above the diaphragm. Also provides for the escape of fuel gas in the event of a diaphragm rupture.

VENTED DECORATIVE APPLIANCES—A vented appliance whose only function lies in the aesthetic effect of the flames. Gas hearth appliances tested to ANSI Standard Z.21.50 include gas fireplaces, fireplace inserts, and freestanding appliances.

VENTING SYSTEM—A continuous open passageway from the flue collar or draft hood of the appliance to the outside atmosphere for the purpose of removing flue gases.

WASH—See Splay

WASHCOAT—Material applied to the substrate of catalytic combustor to increase and maintain surface area. Chemically inert, usually a high surface area alumina.

WATER COLUMN (WC)—Measurement in inches of pressure of gas. 28 inches wc equals one psi.

WATER HEATER—An appliance intended principally for heating domestic (or tap) water.

WET GAS—Unprocessed natural gas containing more than 20% of impurities and heavier hydro-carbons

WYTHE—The masonry wall that must separate multiple flue liners in a masonry chimney. Also referred to as Partition.

ZERO CLEARANCE FIREPLACE—A factory built fireplace that is constructed so that it can be placed safely close to combustible materials.
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